Ionic liquid crystalline materials exhibiting smectic C phase

Article abstract of DOI:10.1080/15421406.2012.688617

Ionic liquid crystalline compounds with a long terminal chain and their nonionic family were synthesized. The ionic liquid crystalline compound (I-7) with a heptyloxy terminal chain exhibited smectic A and C phases. On the other hand, a nonionic family of ionic I-7 showed a smectic A phase. In the case of the ionic liquid crystalline compound (I-4) with a butyloxy terminal chain, a smectic A phase was formed. A nonionic family of ionic I-4 did not show a liquid crystalline phase. The isotropization temperatures of the ionic liquid crystalline compounds were higher when compared to the nonionic family. These results exhibit that the ionic interactions act effectively in forming a liquid crystalline phase with enhanced thermal stability and enable the formation of the fluid smectic phases. In ionic I-7, the formation of the smectic C phase that the nonionic family of I-7 did not exhibit was led through the balance between an anisotropy formed by the mesogenic groups and the ionic interactions. Taylor and Francis Group, LLC.

Full text of DOI:10.1080/15421406.2012.688617

This article was downloaded by: [Texas A&M University Libraries]
On: 27 June 2013, At: 14:32
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Molecular Crystals and Liquid Crystals
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gmcl20
Ionic Liquid Crystalline Materials
Exhibiting Smectic C Phase
Jinzhi Wu a & Seiji Ujiie a
a Department of Applied Chemistry, Faculty of Engineering, Oita
University, 700 Dannoharu, Oita 870-1192, Japan
Published online: 02 Aug 2012.
To cite this article: Jinzhi Wu & Seiji Ujiie (2012): Ionic Liquid Crystalline Materials Exhibiting
Smectic C Phase, Molecular Crystals and Liquid Crystals, 563:1, 67-74
To link to this article: http://dx.doi.org/10.1080/15421406.2012.688617
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary
sources. The publisher shall not be liable for any loss, actions, claims, proceedings,
demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

Mol. Cryst. Liq. Cryst., Vol. 563: pp. 67–74, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.688617
Ionic Liquid Crystalline Materials Exhibiting
Smectic C Phase
JINZHI WU AND SEIJI UJIIE∗
Department of Applied Chemistry, Faculty of Engineering, Oita University,
700 Dannoharu, Oita 870-1192, Japan
Ionic liquid crystalline compounds with a long terminal chain and their nonionic family
were synthesized. The ionic liquid crystalline compound (I-7) with a heptyloxy terminal
chain exhibited smectic A and C phases. On the other hand, a nonionic family of ionic
I-7 showed a smectic A phase. In the case of the ionic liquid crystalline compound (I-4)
with a butyloxy terminal chain, a smectic A phase was formed. A nonionic family of ionic
I-4 did not show a liquid crystalline phase. The isotropization temperatures of the ionic
liquid crystalline compounds were higher when compared to the nonionic family. These
results exhibit that the ionic interactions act effectively in forming a liquid crystalline
phase with enhanced thermal stability and enable the formation of the fluid smectic
phases. In ionic I-7, the formation of the smectic C phase that the nonionic family of
I-7 did not exhibit was led through the balance between an anisotropy formed by the
mesogenic groups and the ionic interactions.
Keywords Ionic liquid crystal; smectic c; terminal alkyl chain; phase transition; x-ray
diffraction
Introduction
Ionic liquid crystals are a key material in the field of self-organized materials. Low-
molecular-weight and polymeric liquid crystals with ionic groups were already synthesized,
and their thermal and orientational properties were examined [1–3]. In the ionic liquid
crystalline compounds, ionic interactions also lead to the formation of liquid crystalline
phases with enhanced thermal stability and induce a microphase separation consisting of
hydrophilic and hydrophobic domains. The ionic liquid crystalline compounds that an
ammonium ion attaches to a mesogenic group through a methylene chain have an ionic
aggregation and an anisotropy through interactions between the mesogenic groups [4–6],
In this case, ionic liquid crystalline compounds have both characteristics of surfactants and
calamitic liquid crystals. The liquid crystalline phases are formed by a balance of the ionic
aggregation and the anisotropy produced by mesogenic groups.
In this study, we synthesized ionic liquid crystals with a long terminal chain and
examined their thermal and orientational properties. The liquid crystalline properties of the
ionic liquid crystals were compared with those of nonionic family. This paper describes the
∗Address correspondence to Prof. Seiji Ujiie, Department of Applied Chemistry, Faculty of
Engineering, Oita University, 700 Dannoharu, Oita 870-1192, Japan. Tel.: 097-554-7903; Fax: 097-
554-7893. E-mail: seujiie@oita-u.ac.jp
67

68
J. Wu and S. Ujiie
formation of a smectic C phase and an effect of the balance between ionic interactions and
an anisotropy in the ionic liquid crystals.
Experimental
Synthesis
Nonionic Compounds. Iminodiethanol and 6-bromo-1-(4-(4-heptyloxy(phenylazo))
phenoxy)hexane were dissolved in 100 mL of 2-propanol, and the solution was reacted
at 120◦C for 35 h. After the reaction, the mixture was cooled to room temperature, and the
precipitated product (nonionic N-7, Fig. 1) was filtered off. 1H NMR(CDCl3), δ: 0.92 (3H,
-CH3), 1.30–1.50 (14H, -CH2-), 1.60 (2H, HO-), 1.81 (4H, -CH2-), 2.57 (2H, N-CH2),
2.65 (2H, N-CH2), 3.62 (4H, HO-CH2), 4.03 (4H, phenyl-O-CH2), 6.99 (4H, phenyl), 7.86
(4H, phenyl).
N-4 with a butyl terminal group was synthesized by the same method as the case of
N-7.
Ionic Compounds. Nonionic N-7 and ethyl iodide was dissolved in 30 mL of 2-propanol,
and the solution was reacted at 120◦C for 50 h. Bis(2-hydroxyethyl)ethyl(6-(4-(4-
heptyloxy(phenylazo))phenoxy)hexyl)ammonium iodide (ionic I-7, Fig. 1) precipitated
from the solution, was filtered off, and was washed with cold 2-propernol. 1H NMR (CDCl3),
δ: 0.88 (3H, -CH3), 1.10 (3H, -CH3), 1.20–1.60 (12H, -CH2-), 1.80 (4H, -CH2-), 2.60 (2H,
-CH2-), 2.94 (2H, -OH), 3.66 (8H, N+-CH2), 4.05 (4H, phenyl-O-CH2), 7.00 (4H, phenyl),
7.85 (4H, phenyl).
I-4 with a butyl terminal group was synthesized by the same method as the case of I-7.
Measurements
Optical textures were observed with a polarizing microscope (Nikon Eclipse LV100POL)
equipped with a hot stage (Mettler Toledo FP90-FP82HT). Phase transitions were mea-
sured by polarizing microscopic observation and DSC measurement (Shimadzu DSC60-
EK90/SH). The orientational behavior was examined by the temperature-variable X-
ray diffraction measurement (Shimadzu XRD-6100), and a possible packing model was
proposed.
Figure 1. Structures of nonionic (N-n; n = 4, 7) and ionic (I-n; n = 4, 7) compounds.

LC Materials Exhibiting Smectic C Phase
69
Table 1. Phase transitions of nonionic and ionic compounds (N-4, N-7, I-4 and I-7)
Sample
N-4
Phase transition temperatures1)/◦C
heating k 110.5 I
cooling k 102.7 I
N-7
I-4
heating k 71.3 SmA 104.9 I
cooling k 70.9 SmA 101.4 I
heating k 117.8 SmA 169.7 I
cooling k 87.3 SmA 146.8 I
I-7
heating k1 46.7 k2 106.5 SmC 116.4 SmA 128.2 I
cooling k1 41.1 k2 100.2 SmC 109.8 SmA 120.8 I
1) k, k1, k2:crystal, SmC:smectic C, SmA:smectic A, I:isotropic.
Results and Discussion
Phase Transitions
Phase transitions of ionic liquid crystalline compounds (I-4, I-7) and those nonionic family
(N-4, N-7) are summarized in Table 1. Ionic I-4 that an ammonium group attaches to a
butyloxyazobenzene mesogenic group through a hexamethylene chain showed a smectic A
phase with a focal conic fan texture and a dark field exhibiting a perpendicular alignment,
which is characterized by a conoscopic interference figure. Ionic I-7 with a heptyloxy
terminal chain exhibited a smectic C phase characterizing by a schlieren texture as well as
a smectic A phase. On the other hand, nonionic N-4 that the ammonium group of ionic I-4
is displaced to an amine group was crystalline and did not show a liquid crystalline phase.
Nonionic N-7 exhibited a smectic A phase. This result for the liquid crystal formation of
ionic and nonionic families indicates that the long terminal chain leads to the enhancement
of a liquid crystal formation ability.
Optical textures of the smectic liquid crystalline phases were shown in Figs. 2–4. A
focal conic fan texture was observed in the smectic A phases of N-7 and I-7 (Figs. 2 and 4).
The smectic C phase of I-7 was characterized by a schlieren texture (Fig. 3). The smectic A-
smectic C phase transition of I-7 was not clear by DSC measurement (Fig. 5). At the smectic
C-smectic A phase transition temperature, however, the schlieren texture changed to the
focal conic fan texture obviously. Moreover, the smectic A-isotropic phase transition was
not observed by DSC measurement. However, N-7 clearly exhibited a smectic A-isotropic
phase transition peak (Fig. 6). The smectic A phase of I-7 was formed in the isotropic
temperature range of N-7, which the interactions between the mesogenic groups act in
forming the smectic A phase. This indicates that the smectic A phase of I-7 was mainly
formed by the ionic interactions between ammonium ions and counterions. Furthermore,
in that temperature range, the interaction between the mesogenic groups is insufficient for
maintaining the smectic A orientation in capability. It becomes impossible for the ionic
interaction to maintain microphase separation with increasing temperature and the layer
structure collapses gradually. Consequently, the smectic A-isotropic phase transition peak
of I-7 is not observed.
X-Ray Diffractions. In general, the X-ray diffraction pattern for a fluid smectic phase such
as smectic A and smectic C phases consists of the sharp inner reflections at the small-angles

70
J. Wu and S. Ujiie
Figure 2. Focal conic texture of smectic A phase of N-7 at 85.4◦C.
and the broad outer reflection in the wide-angle region. N-7, I-4 and I-7 exhibited the X-
ray small-angle reflections and the X-ray wide-angle halo in the smectic A temperature
range (Fig. 7). The same X-ray diffraction patterns were also observed in the smectic
C temperature range (Fig. 7). The layer spacings and extended molecular lengths were
summarized in Table 2. The extended molecular lengths were obtained by using both a
space-filing model and chem3D. Since the formation of the fluid smectic phase is led by
Figure 3. Schlieren texture of smectic C phase of I-7 at 107.0◦C.

LC Materials Exhibiting Smectic C Phase
71
Figure 4. Focal conic texture of smectic A phase of I-7 at 120.0◦C.
ionic aggregations, a hydrophilic sublayer is formed [1,4,5–7]. Moreover, the formation
of the tilted phase occurs by an anisotropy through interactions between the mesogenic
groups with the long alkyl chain. Consequently, the smectic layer is composed of the
hydrophilic and hydrophobic sublayers, and those sublayers alternately pile in the smectic
phase. Possible packing models are shown in Fig. 8. Hydroxyl, ammonium and iodide
groups in the hydrophilic sublayer form hydrogen bonding and ionic interactions. These
interactions enhanced the thermal stability of the hydrophilic sublayer.
Figure 5. DSC curves of I-7 on heating and cooling processes.

72
J. Wu and S. Ujiie
Table 2. Layer spacings and extended molecular length
Layer spacing/nm
Extended
Sample
SmC
SmA
molecular length/nm
N-7
I-4
I-7
—
—
4.55
5.70
4.39
4.97
3.01
2.68
3.01
Figure 6. DSC curves of N-7 on heating and cooling processes.
Figure 7. X-ray diffraction patterns of smectic A (115.0◦C) and smectic C (107.0◦C) phases of I-7.

LC Materials Exhibiting Smectic C Phase
73
Figure 8. Possible packing models of smectic C and smectic A phases of I-7. Ammonium and iodide
ions will be displaced above and below the plane of Fig. 8 to minimize repulsive force.
On the other hand, N-7 showed a smectic A layer spacing corresponding to twice
extended molecular length. This indicates the formation of a bilayer structure in the smectic
A phase as shown in Fig. 9. In this case, a part of the terminal group overlaps each other, and
there is a microphase separation. The packing of N-7, which does not have an ionic group,
is mainly determined by the anisotropy obtained by the interaction between the mesogenic
groups. In the smectic A phases of I-7 and N-7, the molecular orientational structures are
different. Also, the smectic C phase was shown for only I-7. These suggest that the liquid
crystal formation strongly depends on the ionic interactions.
Figure 9. Possible packing model of smectic A phases of N-7.

74
J. Wu and S. Ujiie
Conclusions
The use of ionic interactions led to the formation of the liquid crystalline phase with
enhanced thermal stability. The ionic liquid crystal (I-7) formed the smectic C phase as
well as the smectic A phase. However, the nonionic family (N-7) of I-7 exhibited only
the smectic A phase. This shows that the presence of the ionic interactions enabled the
generation of the smectic C phase. In the smectic C phase, the balance (IIAB) between
the ionic interactions and an anisotropy formed by the mesogenic groups controlled the
structure of the liquid crystalline state. In the smectic A phase, however, I-7 formed the
smectic A phase through the segregation of the ionic and nonionic domains. It is sure that
IIAB is an important factor for molecular designs of the ionic liquid crystals.
References
[1] Ujiie, S., & Iimura, K. (1992). Macromolecules, 25, 3174.
[2] Ujiie, S., Furukawa, H., Yano, Y., & Mori, A. (2006). Thin Solid Films, 509, 185.
[3] Collings, P.J., & Patel, J.S. (Eds.). (1997). Handbook of Liquid Crystal Research, Oxford Uni-
versity Press: Oxford, p 333.
[4] Ujiie, S., & Takagi, S. (1998). High Perform. Polym., 10, 139.
[5] Ujiie, S. & Iimura, K. (1993). Polym. J., 25, 347.
[6] Ujiie, S., Tanaka, Y., & Iimura, K. (2000). Polym. Adv. Technol., 11, 450.
[7] Yoshimi, T., Ujiie, S., & Moriyama, M. (2009). Mol. Cryst. Liq. Cryst., 511, 319.